Arrangement for noise reduction in vacuum systems

ABSTRACT

The present invention relates to an arrangement for adapting the transportation behavior of material to be conveyed, which arrangement comprises a first container, which is coupleable to a first pressure level; a second container, which is coupleable to a second pressure level; a connecting line for transporting material to be conveyed from the first container to the second container; and a pressure reduction device by means of which a pressure difference between the first container and the second container is controllably variable.

This application claims the benefit of the filing date of the GermanPatent Application No. 10 2005 013 566.8 filed Mar. 23, 2005 and of theU.S. Provisional Patent Application No. 60/664,329 filed Mar. 23, 2005,the disclosures of which are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an arrangement and a method foradapting the transportation behavior of material to be conveyed; to ameans of locomotion; and to the use of an arrangement for adapting thetransportation behavior of material to be conveyed in an aircraft.

TECHNOLOGICAL BACKGROUND

The term “vacuum systems” refers to special pneumatic conveyors.Generally speaking, in such conveyors transportation takes place in thata pressure difference is applied to the material to be conveyed, i.e.the material to be conveyed is entrained in the fluid flow generated asa result of the pressure difference, wherein generally air is used asthe transport medium.

Especially in aircrafts, vacuum systems are used for the transportationof waste from the cabin, for example from toilets or galleys, to acentral collecting tank. In this arrangement the material to be conveyedis conveyed to the collecting tank by way of a pipeline network.Negative pressure in the collecting tank in relation to the cabinpressure provides the required pressure difference.

In aircraft with pressurised cabins the pressure difference between thecabin and the environment is used directly to generate the negativepressure for pneumatic conveyance. When this pressure difference isinsufficient, e.g. on the tarmac or at low altitudes, the requiredpressure difference is generated by a compressor.

In the case of toilets with a pneumatic conveyor system in aircraftsystems, often a loud noise level arises. This noise is even noticed bythe passengers in the cabin and is perceived by passengers to beuncomfortable.

Conventional measures to reduce the noise level at the feed-in locationconsist of closing the lid of the conveyance system prior to theflushing procedure so as to thereby keep the noise in check.Furthermore, attempts are made to instruct passengers by way of specificsignage to take noise reduction measures such as for example to closethe toilet lid. Up to now the kinetic energy of the material to beconveyed has been reduced at the inlet to the tank by means of tankinlet protection devices so as to prevent damage and wear.

However, up to now the above-described noise reduction measures havereturned only moderate success, without effectively improving passengercomfort.

SUMMARY OF THE INVENTION

There may be a need to reduce noise generation in a pneumatic system fortransporting a material to be conveyed.

According to an aspect of the invention there is provided an arrangementand a method for adapting the transportation behavior of material to beconveyed; a means of locomotion; and a use of an arrangement foradapting the transportation behavior of material to be conveyed in anaircraft according to the independent claims.

According to an exemplary embodiment of the invention an arrangement foradapting the transportation behavior of material to be conveyed isprovided. The arrangement comprises at least one first container, whichis coupleable to a first pressure level; at least a second container,which is coupleable to a second pressure level; and a connecting linefor transporting material to be conveyed from the first container, ofwhich there is at least one, to the second container, of which there isat least one. Furthermore, the arrangement comprises a pressurereduction device by means of which a pressure difference between thefirst container, of which there is at least one, and the secondcontainer, of which there is at least one, is controllably variable.

According to another exemplary embodiment of the invention a method foradapting the transportation behavior of material to be conveyed iscreated. In this method at least one first container is coupled to afirst pressure level, at least one second container is coupled to asecond pressure level, and material to be conveyed is transported fromthe first container, of which there is at least one, to the secondcontainer, of which there is at least one. Furthermore, a pressurereduction device for varying a pressure difference between the firstcontainer, of which there is at least one, and the second container, ofwhich there is at least one, is controlled.

According to yet another exemplary embodiment of the invention a meansof locomotion with an arrangement with the characteristics describedabove is created.

According to yet another exemplary embodiment of the invention anarrangement for adapting the transportation behavior of material to beconveyed, with the characteristics described above, is used in anaircraft.

According to an embodiment of the invention the noise level during aconveyance procedure can be reduced to such an extent that users (forexample passengers of an aircraft) no longer perceive it negatively.With the arrangement and the method according to embodiments of theinvention noise reduction, in particular as far as aircraft areconcerned, is made possible by an economical and light-weight solution.Further, due to an adaptation of the pressure differences andaccordingly of the transportation velocity, because of a deceleration ofthe fluid there occur less damages caused by the kinetic energy of thematerial to be conveyed. Keeping aircraft weight to a minimum is a veryspecial objective.

In that according to one embodiment of the invention a pressurereduction device is provided in a pneumatic conveyance system, by meansof which pressure reduction device a pressure difference between twocontainers can be controlled in a targeted way and can in particular bereduced, the transport characteristics can be influenced in a definedmanner, in particular the transport speed can be attenuated, as a resultof which noise generation is also reduced to a surprising degree.

The speed of the air at the feed-in location, which air entrains thematerial to be conveyed, largely depends on the position of thereceiving tank in the pipe system and on the pressure in the collectingtank. At the same time this air speed determines the noise that isgenerated. By means of the reduction in the pressure difference noisedevelopment that arises can effectively be reduced.

The large pressure difference between the interior cabin pressure andthe exterior ambient pressure at cruising altitude, which pressuredifference in conventional systems can result in the fluid attainingenormous speeds, can be reduced in a targeted way such that the noisedevelopment at the feed-in location is significantly reduced.

Due to the reduction of the fluid velocity damages in particular at thecontainer walls of the receiving container may be avoided effectively,because the material to be conveyed impinges at the container walls withan accordingly reduced kinetic energy.

It can be achieved that the generated noise level at the feed-inposition and the kinetic energy of the material to be conveyed isreduced by influencing and adapting pressure differences in a conveyancesystem.

In a further exemplary embodiment the pressure reduction devicecomprises at least one ventilation unit between the first container andthe second pressure level. This makes it possible to hold a pressuredifference constant or to compensate any excessive pressure differencein that the pressure in the second container is increased. Thisventilation unit can optionally be designed so as to be regulable ornon-regulated. Furthermore, the ventilation device can comprise noisereduction devices, in particular sound absorbers, so as in this way toreduce the inflow noise from the cabin. In an exemplary embodiment aventilation unit can be installed between the second container and thesecond pressure level and can be controlled in such a way that thematerial to be conveyed can flow from the second pressure level back tothe second container.

In a further exemplary embodiment the pressure reduction devicecomprises at least one throttle element between the first container andthe second pressure level, wherein the throttle element can be designedso as to be either regulable or non-regulated. The throttle element canregulate, i.e. reduce, the fluid speed, and can be installed eitherbetween a ventilation unit and the second pressure level in order toreduce the inflow speed at that location. Alternatively, it can belocated between the second container and the second pressure level inorder to reduce the speed at which the fluid flows out into thesurroundings.

In a further exemplary embodiment the arrangement comprises a compressorelement between the second pressure level and the second container inorder to generate negative pressure in the second container, so that inthe case of a high second pressure level there is nonetheless a pressuredifference between the first container and the second container isprovided, in that for example the pressure in the second container isreduced. Parallel to the compressor element there is the additionaloption of installing a regulable or non-regulated throttle element in aparallel branch so as not to influence the operation of the compressoras a result of the reduction, in other words without causing athrottling effect.

In a further exemplary embodiment a nonreturn valve or a check valve isattached in the connecting line between the second pressure level andthe second container so as to prevent the fluid from flowing in from thesecond pressure level to the second container. The nonreturn valve canalso be installed parallel to the compressor, and furthermore it cancomprise an integrated throttle device.

In a further exemplary embodiment a separator is installed between thesecond container and the pressure level for separating the material tobe conveyed from a fluid.

In a further exemplary embodiment the first container is connected tothe connecting line by means of an actuating valve, wherein afteractuation of the actuating valve transport of the goods to be conveyedcan be started or stopped.

In a further exemplary embodiment noise reduction devices are provided,in particular are installed on the first container.

In a further exemplary embodiment an inlet protection device is affixedin the second container in order to reduce the kinetic energy of thematerial to be conveyed when said material enters the second container.

In a further exemplary embodiment the pressure reduction devicecomprises at least one component with integrated throttle andventilation function between the second pressure level and the secondcontainer.

According to an exemplary embodiment of the invention, in an emergencythe ventilation devices are closed essentially without any auxiliaryenergy, and/or the throttle elements are opened essentially without anyauxiliary energy.

According to a further exemplary embodiment of the method, for thepurpose of controlling the ventilation device and/or the throttleelement the pressure difference between the first container and thesecond container is used as a command variable. In a further exemplaryembodiment of the method, the command variable for controlling theventilation unit and/or for controlling the throttle element can be setdepending on the position of the first containers and/or of the secondcontainers.

According to a further exemplary embodiment of the method the compressorelement and the ventilation device can vary and set the pressure in amanner offset in time before and after conveying the material to beconveyed.

According to an exemplary embodiment of the method, for the purpose ofcontrolling and regulating the ventilation device and/or the throttleelements, sensor data such as for example cabin pressure, ambientpressure, pressure and fill level of the second container, flightaltitude or temperature can be used. This data also makes it possible todiagnose the vacuum system. For example by means of a flushing procedurethat only involves air, and by measuring the resulting tank-pressuregradient, a comparison of the desired values with actual values forpressure losses can take place and in this way any malfunctions can bedetected reliably and early.

The designs of the arrangement also apply to the method and to the meansof locomotion as well as or their use, and vice versa.

The described arrangement and the described method provide effectivenoise reduction of transported material to be conveyed, so that thecomfort, for example of passengers, is enhanced enormously. The kineticenergy can be optimally set with a controllable pressure ratio, as aresult of which optimal setting, damage and noise are prevented orreduced. Furthermore, this arrangement is extremely light in weight andeconomical to implement.

The means of locomotion according to the invention can for example be anaircraft, a rail carriage, a truck, a passenger motor vehicle, acaravan, a boat or ship, or a zeppelin.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, for further explanation and to provide a better understanding ofthe present invention, several embodiments of the invention aredescribed in more detail with reference to the drawings, as follows:

FIG. 1 a diagrammatic view of a vacuum system according to an exemplaryembodiment of the invention;

FIG. 2 a diagrammatic view of a vacuum system according to anotherexemplary embodiment of the invention with variants for regulating thethrough-flow speed;

FIG. 3 a diagram showing the influence which ventilation and throttlinghave on the speed of transportation and on the noise level at thefeed-in location, depending on the magnitude of the air volume in thetank.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Identical or similar components in different figures have the samereference characters.

The illustrations in the figures are diagrammatic and not to scale.

FIG. 1 shows an arrangement of a vacuum system for aircraft with apressurised cabin.

In each case first containers 3 to accommodate a material 2 to beconveyed are connected by means of an actuating valve 4 to a connectingline 5 leading to a central second container 7. Noise reduction devices31 are installed on each of first containers 3. At the inlet to thesecond container 7 there is a special tank inlet protection device 6,which among other thing's is designed to reduce the kinetic energy ofthe material 2 to be conveyed, so as to protect the second container 7.By means of a further connecting line 11 the collecting tank 7 isconnected, by way of a separator 10 which includes a tank return and byway of a compressor element 12, to the second pressure level 14, herethe environment outside the aircraft. Parallel to the compressor element12 a return valve 13 is arranged.

If the pressure difference between the first pressure level 1 (ambientpressure at the feed-in location 3, for example cabin pressure) and thesecond pressure level, i.e. between the cabin 1 and the environment 14,is inadequate, the system is operated with the compressor element 12(operating mode I). In this way the compressor 12 starts at the latestwhen a flushing procedure is requested. During the time interval of afew seconds until the opening of the actuating valve 4, negativepressure is already generated in the second container 7. Thus, as soonas the flush valve 4 is opened, conveyance to the tank, of the material2 to be conveyed, commences. The compressor element 12 continues to runat least until the actuating valve 4 is closed again, thus maintainingnegative pressure in the tank 7 for continuous conveyance. The separator10 prevents any material 2 to be conveyed from escaping from thecollecting container 7, and protects the compressor 12 and theenvironment 14 from contamination. The nonreturn valve 13 remains closedin this operating mode.

In an alternative operating mode II with sufficient pressure differencebetween the cabin 1 and the environment 14 the compressor element 12remains switched off. When the actuating valves 4 are closed, the tank 7is subjected to the same low pressure as in the environment 14 outsidethe aircraft. If the flush valve 4 is open, negative pressure in thetank 7 is maintained in that the air flows out by way of the nonreturnvalve 13.

Up to now the compressor elements 12 have mostly been designed so as toprovide just adequate conveyance behavior when the aircraft is on theground. The nonreturn valve can already fully open at a small pressuredifference, and the airflow through it can take place with minimum lossof pressure. Downstream of the separator 10 a non-regulated throttledevice 15 a is provided for easy adaptation of the conveyance behavior.However, generally speaking, this throttling position cannot beconsidered optimal for all forms of application because part of theexpensively generated pressure difference is degraded during compressoroperation 12.

In FIG. 2 a further arrangement for reducing noise at the feed-inlocations of the material 2 to be conveyed has been provided by limitingthe driving pressure difference to an extent necessary for the flushingprocedure, preferably in operating mode II.

For reliable operation, this design point should be above the behaviorwith compressor operation. This still leaves sufficient potential toreduce noise at cruising altitude, at which normally the maximumpressure difference occurs. This applies in particular since in mostcases this state represents the main share of the time vacuum systems inaircraft are used.

Essentially the air volume 9 in the collecting tank 7 causes anon-stationary pressure gradient in the second container 7 during theflushing procedure. Thus, most of the time, the pressure in thecollecting tank 7 increases until the stationary state has been reached.This increase in pressure is determined by the flow losses from 9 to 14in the stationary case. The pressure difference between the cabin 1 andthe collecting tank 7 induces a corresponding time gradient of the airentry speed, and thus of the generated noise level at the firstcontainer 3.

In order to limit noise emission, an essentially constant pressuredifference from 1 to 7 has to be ensured. Generally speaking anadditional ventilation valve 16 a-16 d according to FIG. 2 can handlethis task before, during and after the flushing procedure. However, thiscan be associated with high speeds or high volume flows between theconnecting lines 5 or 11 or the tank 7 and the ventilation valve 16 a-16d. This can be compensated for by using a further regulable throttlevalve 17 a or 17 b downstream of the ventilation valve 16 a-16 d. If athrottle valve 15, 17 is used on its own, its influence is howeverlimited to the duration of the flushing process.

The greater the air volume 9 in the tank, the stronger the effect theinitial tank pressure has on the flushing process. In this case astationary state only occurs after a relatively long opening time of theflush valve 4 (compare FIG. 3). Thus in this case ventilation assumesdecisive importance.

In such a cases where a small second container 7 is used, the air volume9 is small. It may thus be possible to abandon a ventilation valve 16a-16 d. In the case of a small number of connected receiving containers3, which are installed at similar distances from the tank 7, it is alsopossible to provide a non-regulated throttling element, for example atposition 15 b. At this position, compressor operation 12 is not affectedby the reduction. Reduced conveyance performance at low flightaltitudes, i.e. at small pressure differences, without compressoroperation 12 can also be compensated for by extending compressoroperation if need be. Moreover, the use of the system in this boundaryregion does not represent a typical application case.

In principle the actuating valve 16 can be installed at positions 16a-16 d. Immediately after a request of a flushing procedure saidactuating valve 16 sets the required tank pressure until the flush valve4 is opened. This procedure can be interpreted as a counterpart to theevacuation phase during compressor operation 12. Subsequently, forexample, the throttle valve keeps the tank pressure constant at position17 a or 17 b during the flushing procedure.

Since the loss of pressure 1-9 depends on the length and the gradient ofthe connecting line 5, the pressure difference to be set should beimplemented depending on the position of the first container 3. In thisway the often very different transportation behavior of receivingcontainers 3 with different distances from the collecting tank 7 can bemade to be uniform.

In the case of malfunction a ventilation valve 16 should assume a fullyclosed state, while a regulable throttle valve 17 should assume a fullyopen state, both without any auxiliary energy. In this way the systemremains functional.

Also of interest is the combination of ventilation function and throttlefunction at positions 16 d and 17 a to a component.

As far as regulation is concerned, access to data that is alreadyavailable in the aircraft system presents itself; such data being forexample cabin pressure, ambient pressure and tank fill level (todetermine the air volume in the tank). Furthermore, fill leveldetermination based on two absolute pressure sensors directly providesinformation on the pressure in the tank 7. As shown in FIG. 2, a sensor32 is positioned in line between first container 3 and second container7. A monitoring device 33 is coupled to sensor 32. The sensor 32 andmonitoring device 33 may also or alternatively be positioned in the tank7. The use of additional sensors can thus be minimised by suitablesystem linkages.

From the regulating deviations for a flushing procedure that onlyinvolves air, it is furthermore possible to obtain informationconcerning possible blockages in the regions 1-9 and 9-14. Thisdiagnostic function can also be transferred to conventional vacuumsystems.

In addition it should be pointed out that “comprising” does not excludeother elements or steps, and “a” or “one” does not exclude a pluralnumber. Furthermore, it should be pointed out that characteristics orsteps, which have been described with reference to one of the aboveembodiments can also be used in combination with other characteristicsor steps of other embodiments described above.

It should also be noted that reference signs in the claims shall not beconstrued as limiting the scope of the claims.

The invention claimed is:
 1. An arrangement for an aircraft for adaptingthe transportation behavior of material to be conveyed, wherein thearrangement comprises: at least one first container coupleable to afirst pressure level; at least one second container coupleable to asecond pressure level; a connecting line for transporting material to beconveyed from the at least one first container to the at least onesecond container; a first actuating valve for coupling the at least onefirst container to the connecting line; a pressure reduction device fornoise reduction wherein the pressure reduction device comprises at leastone controllably variable ventilation unit, the pressure reductiondevice being at or downstream of the at least one second container,wherein the at least one ventilation unit is configured to control thepressure difference between the first pressure level and the at leastone second container; and wherein the pressure in the at least onesecond container is configured to be increased before changing the firstactuating valve from a closed state to an open state, which open stateis adapted to start the transportation process such that the pressuredifference between the first pressure level and the at least one secondcontainer is kept constant to generate a constant suction fortransporting the material to be conveyed and the transport speed of thematerial to be conveyed is reduced, as a result of which noisegeneration is reduced; a compressor element between the second pressurelevel and the at least one second container to generate negativepressure in the at least one second container if the pressure differencebetween the first pressure level and the second pressure level is notsufficient for transporting the material.
 2. The arrangement accordingto claim 1, wherein the at least one ventilation unit is configured soas to be regulable or non-regulated.
 3. The arrangement according toclaim 1, wherein the at least one ventilation unit comprises a noisereduction device comprising a sound absorber.
 4. The arrangementaccording to claim 1, further comprising at least one throttle elementinstalled between the at least one ventilation unit, and the at leastone second container or the connecting line.
 5. The arrangementaccording to claim 1, further comprising a separator installed betweenthe at least one second container and the second pressure level, saidseparator being configured to accommodate material to be conveyed, sothat transport of material to be conveyed from the at least one secondcontainer to the second pressure level is prevented, and wherein the atleast one ventilation unit is installed between the second container andthe separator.
 6. The arrangement according to claim 1, furthercomprising a plurality of noise reduction devices installed on the atleast one first container.
 7. The arrangement according to claim 1,further comprising an inlet protection device affixed in a boundaryregion between the connecting line and the at least one secondcontainer.
 8. The arrangement according to claim 1, wherein the pressurereduction device further comprises a component with integrated throttleand ventilation function between the second pressure level and the atleast one second container.
 9. The arrangement according to claim 1,further comprising a sensor for detecting at least one transportcharacteristic of material to be conveyed between the at least one firstcontainer and the at least one second container.
 10. The arrangementaccording to claim 9, further comprising a monitoring device coupled tothe sensor and configured for, based on at least one transportcharacteristic detected by the sensor, determining the functionabilityof the arrangement.
 11. The arrangement according to claim 1, whereinthe pressure reduction device further comprises at least one throttleelement between the at least one first container and the second pressurelevel.
 12. The arrangement according to claim 11, wherein the at leastone throttle element is either regulable or non-regulated.
 13. Thearrangement according to claim 1, wherein the at least one controllablyvariable ventilation unit is installed directly to or downstream of theat least one second container.
 14. The arrangement according to claim 1,wherein a regulable or non-regulated throttle element is connectedparallel to the compressor element.
 15. The arrangement according toclaim 14, wherein the throttle element is installed between the at leastone second container and the second pressure level.
 16. The arrangementaccording to claim 1, further comprising a nonreturn valve in aconnecting line between the second pressure level and the at least onesecond container.
 17. The arrangement according to claim 16, wherein thenonreturn valve comprises an integrated throttle element.
 18. A methodfor an aircraft for adapting the transportation behavior of material tobe conveyed, comprising: coupling at least one first container to afirst pressure level; coupling at least one second container to a secondpressure level; maintaining a constant pressure difference between thefirst pressure level and the at least one second container to generate aconstant suction for transporting material to be conveyed; transportingmaterial to be conveyed, from the at least one first container to the atleast one second container, via a connecting line, wherein a firstactuation valve couples the at least one first container to theconnecting line; controlling a pressure reduction device for noisereduction wherein the pressure reduction device comprises at least onecontrollably variable ventilation unit, wherein by the at least oneventilation unit the pressure difference between the first pressurelevel and the at least one second container is controlled and thepressure in the at least one second container is increased beforechanging the first actuating valve from a closed state to an open state,which open state is adapted to start the transportation process suchthat the transport velocity of the material to be conveyed is reduced,as a result of which noise generation is reduced, the pressure reductiondevice being at or downstream of the at least one second container;reducing the pressure in the at least one second container by acompressor element, if the pressure difference between the firstpressure level and the second pressure level is not sufficient fortransporting the material.
 19. The method according to claim 18, whereinby the pressure reduction device a transport speed of material to beconveyed is reduced, as a result of which noise generation at the firstcontainer is reduced.
 20. The method according to claim 19, wherein inthe case of a malfunction the pressure reduction device is essentiallyclosed without any auxiliary energy.
 21. The method according to claim19, wherein for the purpose of controlling the at least one ventilationunit the pressure difference between the at least one first containerand the at least one second container is used as a command variable. 22.The method according to claim 21, wherein the command variable forcontrolling the at least one ventilation unit is set depending on theposition of the at least one first container and the at least one secondcontainer.
 23. The method according to claim 19, wherein sensor datarequired for regulating the at least one ventilation unit is selectedfrom the group consisting of cabin pressure data, ambient pressure data,fill level data, air volume, flight altitude data, and temperature dataof the at least one second container.
 24. The method according to claim23, wherein from the sensor data desired values and actual values fromthe measured tank pressure gradient, are compared to diagnosemalfunctions.
 25. The method according to claim 23, wherein the sensordata is air volume of the at least one second container.
 26. The methodaccording to claim 18, wherein by the at least one ventilation unitarranged between the at least one second container and the secondpressure level, the pressure is controlled in such a way that a flow ofthe material to be conveyed, into the at least one second container ismade possible.
 27. The method according to claim 18, wherein in the caseof a malfunction the at least one ventilation unit is essentially closedwithout any auxiliary energy.
 28. The method according to claim 18,wherein the pressure is altered and set by the compressor element andthe at least one ventilation unit in a manner offset in time before andafter conveying the material to be conveyed.
 29. The method according toclaim 18, wherein the at least one controllably variable ventilationunit is installed directly to or downstream of the at least one secondcontainer.
 30. An aircraft comprising an arrangement for adapting thetransportation behavior of material to be conveyed, wherein thearrangement comprises: at least one first container coupleable to afirst pressure level; at least one second container coupleable to asecond pressure level; a connecting line for transporting material to beconveyed from the at least one first container to the at least onesecond container; a first actuating valve for coupling the at least onefirst container to the connecting line; a pressure reduction device fornoise reduction wherein the pressure reduction device comprises at leastone controllably variable ventilation unit, the pressure reductiondevice being at or downstream of the at least one second container,wherein the at least one ventilation unit is configured to control thepressure difference between the first pressure level and the at leastone second container; and wherein the pressure in the at least onesecond container is configured to be increased before changing the firstactuating valve from a closed state to an open state, which open stateis adapted to start the transportation process such that the pressuredifference between the first pressure level and the at least one secondcontainer is kept constant to generate a constant suction fortransporting the material to be conveyed and the transport speed of thematerial to be conveyed is reduced, as a result of which noisegeneration is reduced; a compressor element between the second pressurelevel and the at least one second container to generate negativepressure in the at least one second container if the pressure differencebetween the first pressure level and the second pressure level is notsufficient for transporting the material.
 31. The aircraft according toclaim 30, wherein the at least one controllably variable ventilationunit is installed directly to or downstream of the at least one secondcontainer.